Epoxy work on seats sheer and Zip parts

The last post left off with my having cut out a piece of Meranti for the rear seat. This weekend, I laminated that onto the A/C exterior plywood... and did a little more epoxy work along the way.

1/4" Meranti top for the rear seat

Just as Id done with the front thwart, I coated both mating sides with epoxy (not thickened), and held them together with concrete blocks and weights while the epoxy cured. I had just enough epoxy left over to also add a 2nd layer to the Zip transom knee.

Laminating the Meranti onto the rear thwart. I used the extraneous epoxy to encapsulate the underside of the front thwart, as well as the transom knee for the Zip.

Regrettably, however... after the epoxy cured, there remained a small gap.

And a dust bunny got stuck in the epoxy on the Zip part.

All this didnt go perfectly according to plan. After the epoxy had cured, I found a gap between the two layers that would need to be filled. Also, some dust had gotten stuck in the epoxy on the Zip transom knee. I am trying for substantially better fit and finish on the Zip, so I sanded off the dust bunny & planned to encapsulate with a third layer.

Logistically, I thought it best to encapsulate the undersides of both seats next. This would be the 2nd coat for the forward thwart. I planned to tilt the rear thwart just a little so that epoxy would run into the gap and fill it. Since I havent trimmed the Meranti top yet, this should help the epoxy flow down into the gap. With the extraneous epoxy, I planned to encapsulate the underside of the sheers on the aft third of the boat, as well as the Zip part.

I ended up having more left over epoxy than expected. So after quickly cleaning them off, I also encapsulated part of the Zip stem and the forward face of frame 5-1/2.

More encapsulation; trying to fill the gap on the aft thwart. Here it is propped up slightly with a scrap of mahogany left over from the quarter knees.

Epoxy drying on the Zip stem & frame 5-1/2.

Current Status of Zip Parts
Part	Status
Stem & Breasthook Assembly	Most surfaces have 1 coat of epoxy
Frame 5-1/2	Forward face has 2 layers of epoxy. Other surfaces have 1 layer.
Frame 4	Side members cut, but have not been planed or notched for sheer.
Transom Knee	Coated with 3 layers of epoxy
Transom	Side frame members cut 1/4" oversized on outer side. Have not been planed.

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1 seat attached 1 seat coated Primer finally on sheer

Well, the title kinda says it all. So, lets get right to the pictures:

Here is the trimmed rear thwart, waiting for its first "finish" coat of epoxy on top. The plan was to mix some epoxy, coat the thwart using a thin foam roller, squeegee it, then thicken the rest of the epoxy with silica for attaching the forward thwart permanently.

I taped off areas on and around the forward thwart, to both mark where to place thickened epoxy and to make clean-up go more smoothly.

As you can see, there is a considerable gap between the thwart and the side of the hull on the starboard side. The gap is several inches long & gets progressively wider aft. The joint at the forward edge is considerably better. I knew it would take big globs of VERY thick epoxy to fill this gap.

The gap on the port side wasnt so bad.

First epoxy coat rolled & sqeegeed onto the aft thwart.

Heres that big gap filled with thickened epoxy. Before removing the tape, I used the curved corner of the squeegee to shape the epoxy edges.

Improvised bracing to help make sure the thwart was pressed down solidly and level.

Improvised bracing to help make sure the thwart was pressed down solidly and level.

I wanted to get a photo of this filled gap before I painted over it. This is from where I had to remove some material from the corner of the outer sheer lamination in order to get it to bend into place. I removed a little too much, leaving this gap. During installation of the sheer, I heaped on the thickened epoxy in order to fill it. This is the port side joint between the sheer and transom.

First layer of the AquaGard 190 primer on the port sheer.

First layer of the AquaGard 190 primer on the port sheer.

First layer of the AquaGard 190 primer on the port sheer.

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Old Boat Reverse Sheer

I know what youre thinking. That boat was warped on account of that concrete pillar coming out of the cockpit. But not so. The concrete pillar coming out of the cockpit is an accident of framing.  I could tell when I was taking the picture that maybe my framing was not that good, but I was not in the mood to reposition the boat just for a picture.
Anyway, what I am trying to show here, and it may be more obvious if you click on the photo to see a larger version of it, is that the sheer line has gone into reverse, that is, the sheer is higher in the middle than at the ends. And the bottom of the boat has flattened out to the point of almost no rocker. 
The sheer line for the non-nautical is the line made by the tops of the gunwales, that is, the two boards that form the edge of the deck.
This was not a boat I built, but I am sure that when it was built, it had more sheer and rocker and that the downward movement of the bow and stern with respect to the middle of the boat was the result of the nylon skin tightening up over time. 
The other thing I noticed when I build boats is that since both the keelson and the stringers are bent into place over the ribs, they exert a downward force on the ends of the kayak that combined with the force of a shrinking skin will tend to make the keel line of a skin on frame boat more straight over time.
I am theorizing here, but the Unangan (Aleut) builders always built their keelsons in two or three parts and the parts were carved into a curved shape, not bent into place to avoid this kind of downward pressure on the ends of the boat. 

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